U.S. patent application number 09/969565 was filed with the patent office on 2003-04-03 for silicone pressure sensitive adhesive compositions.
Invention is credited to Kosal, Jeffrey Alan.
Application Number | 20030065086 09/969565 |
Document ID | / |
Family ID | 25515681 |
Filed Date | 2003-04-03 |
United States Patent
Application |
20030065086 |
Kind Code |
A1 |
Kosal, Jeffrey Alan |
April 3, 2003 |
SILICONE PRESSURE SENSITIVE ADHESIVE COMPOSITIONS
Abstract
A pressure sensitive adhesive emulsion comprises a disperse
silicone phase emulsified in a continuous water phase in the
presence of a surfactant. The disperse silicone phase comprises
40-80 percent by weight of a silicone pressure sensitive adhesive,
which is the product of mixing a silanol-terminated
polydiorganosiloxane of Tg below -20.degree. C. with a
silanol-containing silicone resin of Tg above 0.degree. C.,
dispersed in 60-20 percent by weight of a volatile silicone fluid
having a boiling point below 300.degree. C. The emulsion is
substantially free of any non-silicon atom containing volatile
organic material.
Inventors: |
Kosal, Jeffrey Alan;
(Midland, MI) |
Correspondence
Address: |
DOW CORNING CORPORATION CO1232
2200 W. SALZBURG ROAD
P.O. BOX 994
MIDLAND
MI
48686-0994
US
|
Family ID: |
25515681 |
Appl. No.: |
09/969565 |
Filed: |
October 1, 2001 |
Current U.S.
Class: |
524/588 |
Current CPC
Class: |
C08L 83/00 20130101;
C09J 183/04 20130101; C08J 2383/04 20130101; C08J 3/03 20130101;
C09J 183/04 20130101; C08L 83/00 20130101 |
Class at
Publication: |
524/588 |
International
Class: |
C08J 003/00 |
Claims
1. A pressure sensitive adhesive emulsion comprising a disperse
silicone phase emulsified in a continuous water phase in the
presence of a surfactant; the disperse silicone phase comprising
40-80 percent by weight of a silicone pressure sensitive adhesive,
the silicone pressure sensitive adhesive being the product obtained
by mixing a silanol terminated polydiorganosiloxane of Tg below
-20.degree. C. with a silanol containing silicone resin of Tg above
0.degree. C., the silicone pressure sensitive adhesive being
dispersed in 60-20 percent by weight of a volatile silicone fluid
having a boiling point below 300.degree. C.; the emulsion being
free of any non-silicon atom containing volatile organic
material.
2. A pressure sensitive adhesive emulsion according to claim 1
wherein the silicone pressure sensitive adhesive is the product of
mixing 30-60 parts by weight of a silanol-terminated
polydiorganosiloxane of Tg below -20.degree. C. and viscosity
0.1-30000 Pa.s at 25.degree. C. with 40-70 parts by weight of a
silanol-containing silicone resin of Tg above 0.degree. C.
comprising monovalent trihydrocarbonsiloxy (M) groups of the
formula R".sub.3SiO.sub.1/2 and tetrafunctional (Q) groups
SiO.sub.4/2 wherein R" denotes a monovalent hydrocarbon group
having 1 to 6 carbon atoms, the number ratio of M groups to Q
groups being in the range 0.5:1 to 1.2:1.
3. A pressure sensitive adhesive emulsion according to claim 2
wherein the silanol-terminated polydiorganosiloxane has a viscosity
of 1-100 Pa.s at 25.degree. C.
4. A pressure sensitive adhesive emulsion according to claim 1
wherein the said product of mixing has been chemically treated to
react silanol groups with an endblocking agent which introduces
triorganosilyl units.
5. A pressure sensitive adhesive emulsion according to claim 1
wherein the surfactant comprises at least one nonionic
surfactant.
6. A pressure sensitive adhesive emulsion according to claim 5
wherein the surfactant comprises a mixture of an anionic surfactant
and a nonionic surfactant.
7. A pressure sensitive adhesive emulsion according to claim 1
wherein the volatile silicone fluid comprises
decamethylcyclopentasiloxane.
8. A pressure sensitive adhesive emulsion according to claim 1
wherein the volatile silicone fluid comprises
octamethylcyclotetrasiloxane.
9. A pressure sensitive adhesive emulsion according to claim 1
wherein the volatile silicone fluid comprises linear
polydimethylsiloxane of viscosity 0.65 to 3.0 cSt at 25.degree.
C.
10. A process for the production of a pressure sensitive adhesive
emulsion according to claim 1 comprising mixing the silicone
pressure sensitive adhesive and the volatile silicone fluid with
the surfactant and adding water while shearing to form an
emulsion.
11. A process according to claim 10 wherein the water which is
added contains a surfactant.
12. A process according to claim 11 wherein the surfactant which is
added in the water is more hydrophilic than the surfactant which is
mixed with the silicone pressure sensitive adhesive and the
volatile silicone fluid
13. A process for the production of a pressure sensitive adhesive
emulsion according to claim 1 comprising mixing the silicone
pressure sensitive adhesive with the volatile silicone fluid and
adding the resulting mixture to an aqueous solution of the
surfactant while shearing.
14. A process for the production of a pressure sensitive adhesive
emulsion of reduced volatile content wherein an emulsion according
to claim 1 is subjected to steam stripping.
15. A process for the production of a pressure sensitive adhesive
emulsion of reduced volatile content, wherein an emulsion according
to claim 1 is heated with removal of volatile material while adding
water to the emulsion to compensate for water which is removed.
16. A process for the production of a pressure sensitive adhesive
emulsion of reduced volatile content wherein an emulsion according
to claim 1 is contacted with a hydrophobic pervaporation membrane.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
REFERENCE TO A MICROFICHE APPENDIX
[0003] Not applicable.
FIELD OF THE INVENTION
[0004] This invention is related to silicone pressure sensitive
adhesive compositions, and particularly to such compositions in the
form of aqueous dispersions or emulsions. Silicone pressure
sensitive adhesives are used for example in paper coatings, as
release modifying additives to organic pressure sensitive adhesives
and in medical and personal care applications.
BACKGROUND OF THE INVENTION
[0005] U.S. Pat. No. 4,791,163 (Dec. 13, 1988) describes an aqueous
emulsion comprising an organic pressure sensitive adhesive and a
silicone pressure sensitive adhesive. Japanese Patent 07331220
(Dec. 19, 1995) describes an aqueous silicone emulsion adhesive
composition comprising an alkenyl organopolysiloxane, a resin
comprising triorganosiloxy units and SiO.sub.2 units (MQ resin), an
organohydrogenpolysiloxane, an emulsifier and a platinum
catalyst.
[0006] U.S. Pat. No. 5,612,400 (Mar. 18, 1997) describes a silicone
pressure sensitive adhesive composition comprising 100 parts of an
organopolysiloxane of viscosity at least 500000 cps, 60 to 300
parts of a MQ resin having 0.2 to 5 percent silicon-bonded hydroxyl
radicals and a ratio of 0.6-1.2:1 triorganosiloxy units to
SiO.sub.2 units, and 20-2500 parts of a linear or cyclic volatile
organosiloxane fluid of boiling point 95-250.degree. C.
[0007] U.S. Pat. Nos. 5,330,747 (Jul. 19, 1994) and 5,451,610 (Sep.
19, 1995) describe personal care preparations, particularly eye
cosmetics such as mascara, comprising a trimethylsilyl-endblocked
benzene-soluble resinous copolymer containing silicon-bonded
hydroxyl radicals, a silanol-endblocked polydiorganosiloxane fluid
and a phenyl-containing polysiloxane fluid of viscosity 5-60000
centiStokes at 25.degree. C. The composition can optionally contain
a volatile silicone such as hexamethyldisiloxane or
octamethylcyclotetrasiloxane.
BRIEF SUMMARY OF THE INVENTION
[0008] A pressure sensitive adhesive emulsion according to the
invention comprises a disperse silicone phase emulsified in a
continuous water phase in the presence of a surfactant, wherein the
disperse silicone phase comprises 40 to 80 percent by weight of a
silicone pressure sensitive adhesive, which is the product of
mixing a silanol-terminated polydiorganosiloxane of Tg below
-20.degree. C. with a silanol-containing silicone resin of Tg above
0.degree. C., dispersed in 60 to 20 percent by weight of a volatile
silicone fluid having a boiling point below 300.degree. C., the
emulsion being substantially free of any non-silicon-containing
volatile organic material.
[0009] The invention also includes a process for the production of
a pressure sensitive adhesive emulsion comprising mixing the
silicone pressure sensitive adhesive defined above, the volatile
silicone fluid having a boiling point below 300.degree. C., and a
surfactant, and adding water optionally containing surfactant while
shearing to form an emulsion.
[0010] The invention also includes a process for the production of
a pressure sensitive adhesive emulsion comprising mixing the
silicone pressure sensitive adhesive defined above with the
volatile silicone fluid having a boiling point below 300.degree. C.
and adding the resulting mixture to an aqueous solution of a
surfactant while shearing.
[0011] The invention further includes methods for the production of
a pressure sensitive adhesive emulsion of reduced volatile content,
wherein an emulsion as defined above is subjected to steam
stripping, or is contacted with a hydrophobic pervaporation
membrane, or is heated with removal of volatile material while
adding water to the emulsion to compensate for water which is
removed.
[0012] These and other features of the invention will become
apparent from a consideration of the detailed description.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0013] Not applicable.
DETAILED DESCRIPTION OF THE INVENTION
[0014] The silicone pressure sensitive adhesive generally comprises
the product of mixing a silanol-terminated polydiorganosiloxane of
Tg below -20.degree. C. lightly crosslinked with a
silanol-containing silicone resin of Tg above 0oC. The organic
substituents of the silanol-terminated polydiorganosiloxane are
generally alkyl groups having 1 to 6 carbon atoms or phenyl groups.
Preferably at least 80 percent of the organic substituents are
methyl groups. Most preferably the silanol-terminated
polydiorganosiloxane is a dimethylhydroxy-terminated
polydimethylsiloxane. The silanol-terminated polydiorganosiloxane
preferably has a viscosity of at least 0.1 Pa.s and can have
viscosity up to 30000 Pa.s or higher. It can for example be
prepared by the method of U.S. Pat. No. 5,319,120.
[0015] The silanol-containing silicone resin is generally a
non-linear siloxane resin and preferably consists of siloxane units
of the formula R'.sub.aSiO.sub.4-a/2 wherein R' denotes a hydroxyl,
hydrocarbon or hydrocarbonoxy group and wherein a has an average
value of from 1 to 1.8. The resin preferably consists of monovalent
trihydrocarbonsiloxy (M) groups of the formula R".sub.3SiO.sub.1/2
and tetrafunctional (Q) groups SiO.sub.4/2 wherein R" denotes a
monovalent hydrocarbon group having 1 to 6 carbon atoms, preferably
a methyl group. The number ratio of M groups to Q groups is
preferably in the range 0.5:1 to 1.2:1 (equivalent to a value of a
in the formula R'.sub.aSiO.sub.4-a/2 of 1.0 to 1.63), and is more
preferably 0.6:1 to 0.9:1. The silicone resin preferably contains
at least 0.2 percent by weight up to about 3 or 5 percent
silicon-bonded hydroxy radicals. These are preferably present as
dimethylhydroxysiloxy (HO)(CH3).sub.2SiO.sub.1/2 units.
[0016] The silicone pressure sensitive adhesive preferably
comprises 20 to 80 parts by weight, preferably 30 to 60 parts, of
the silanol-terminated polydiorganosiloxane of Tg below -20.degree.
C., and 80 to 20 parts by weight, preferably 70 to 40 parts, of the
silanol-containing silicone resin of Tg above 0.degree. C. Most
preferably the silicone pressure sensitive adhesive is the product
of mixing 30 to 60 parts by weight of a silanol-terminated
polydiorganosiloxane of Tg below -20.degree. C. and viscosity
0.1-30000 Pa.s at 25.degree. C. with 40 to 70 parts by weight of a
silanol-containing silicone resin of Tg above 0.degree. C.
comprising monovalent trihydrocarbonsiloxy (M) groups of the
formula R".sub.3SiO.sub.1/2 and tetrafunctional (Q) groups
SiO.sub.4/2 wherein R" denotes a monovalent hydrocarbon group
having 1 to 6 carbon atoms, the number ratio of M groups to Q
groups being in the range 0.5:1 to 1.2:1.
[0017] The silanol groups of the polydiorganosiloxane generally
undergo some condensation reaction with the silanol groups of the
silicone resin so that the polydiorganosiloxane is lightly
crosslinked by the silicone resin (that is, polydiorganosiloxane
chains are bonded together through resin molecules to give chain
branching and entanglement and/or a small amount of network
character) to form the silicone pressure sensitive adhesive. A
catalyst, for example an alkaline material such as ammonia,
ammonium hydroxide or ammonium carbonate can be mixed with the
silanol-terminated polydiorganosiloxane and the silicone resin to
promote this crosslinking reaction. It may for example be
preferred, particularly for personal care and medical applications,
that the silanol-terminated polydiorganosiloxane has a viscosity in
the range 1-100 Pa.s at 25.degree. C. and is crosslinked with the
aid of a catalyst. The amounts of silanol-terminated
polydiorganosiloxane and silanol-containing silicone resin are
preferably such that the Tg of the product of mixing is between -15
and 15.degree. C. (T at tan delta maximum). The silanol-containing
silicone resin preferably lowers the rubbery plateau modulus (G' at
Tg+30.degree. C.) of the blend below 7E+05 dyne/cm2; this is an
indication that the network character is due to light crosslinking
as discussed above rather than extensive crosslinking.
[0018] The silicone pressure sensitive adhesive produced by mixing
the silanol-terminated polydiorganosiloxane and silanol-containing
silicone resin may be chemically treated to react silanol groups
with an endblocking agent which introduces triorganosilyl units, as
described in U.S. Pat. No. 4,655,767. The endblocking agent can for
example be a disilazane such as hexamethyldisilazane or a trialkyl
alkoxy silane such as trimethyl ethoxy silane or trimethyl methoxy
silane. Reaction with such an end blocking agent reduces the
sensitivity of the adhesive to loss of adhesion in contact with
reagents such as amines.
[0019] The volatile silicone fluid of boiling point below
300.degree. C. can be a linear or cyclic polysiloxane, preferably a
polydiorganosiloxane in which the organo groups are hydrocarbon
groups having 1 to 6 carbon atoms, and most preferably a
polydimethylsiloxane. Examples of suitable linear polysiloxanes are
hexamethyldisiloxane, octamethyltrisiloxane,
decamethyltetrasiloxane and/or dodecamethylpentasiloxane. Examples
of suitable cyclic polysiloxanes are decamethylcyclopentasiloxane,
octamethylcyclotetrasiloxane and/or dodecamethylcyclohexasiloxane.
Mixtures of linear and/or cyclic polydimethylsiloxanes can be used,
for example mixtures of viscosity from 0.65 up to 3.0 or 4.0 cSt at
25.degree. C.
[0020] The volatile silicone fluid is preferably used at 30-150
percent by weight, most preferably 50-100 percent, based on the
silicone pressure sensitive adhesive (blend of silanol-terminated
polydiorganosiloxane and silanol-containing silicone resin). The
volatile silicone fluid allows the silicone pressure sensitive
adhesive to be processed as a liquid of handleable viscosity so
that it can be emulsified, without introducing undesirable volatile
organic hydrocarbons such as toluene or xylene.
[0021] The surfactants may be selected from anionic, cationic,
nonionic or amphoteric surfactants. Mixtures of one or more of
these may also be used. Suitable anionic organic surfactants
include alkali metal soaps of higher fatty acids, alkyl aryl
sulphonates, for example sodium dodecyl benzene sulphonate, long
chain (fatty) alcohol sulphates, olefin sulphates and sulphonates,
sulphated monoglycerides, sulphated esters, sulphonated ethoxylated
alcohols, sulphosuccinates, alkane sulphonates, phosphate esters,
alkyl isethionates, alkyl taurates and/or alkyl sarcosinates.
Suitable cationic organic surfactants include alkylamine salts,
quaternary ammonium salts, sulphonium salts and phosphonium salts.
Suitable nonionic surfactants include siloxane polyoxyalkylene
copolymers, condensates of ethylene oxide with a long chain (fatty)
alcohol or (fatty) acid, for example a C.sub.12-16 alcohol,
condensates of ethylene oxide with an amine or an amide,
condensation products of ethylene and propylene oxides, esters of
glycerol, sucrose or sorbitol, fatty acid alkylol amides, sucrose
esters, fluoro-surfactants and fatty amine oxides. Suitable
amphoteric organic detergent surfactants include imidazoline
compounds, alkylaminoacid salts and betaines. It is more preferred
that the organic surfactants are nonionic or anionic. Mixtures of
anionic and nonionic surfactants are particularly preferred.
[0022] A preferred process for the production of the pressure
sensitive adhesive emulsion is an inversion process comprising
mixing the silicone pressure sensitive adhesive and the volatile
silicone fluid with the surfactant and adding water while shearing
to form an emulsion. The water which is added can be merely water
but preferably contains surfactant. The surfactant added with the
water can be the same as or different to the surfactant mixed with
the silicone pressure sensitive adhesive and the volatile silicone
fluid. Most preferably the surfactants are different, with the
surfactant which is added in the water is more hydrophilic than the
surfactant which is mixed with the silicone pressure sensitive
adhesive and the volatile silicone fluid. We have found that the
best way to make an inversion emulsion of the pressure sensitive
adhesive is to have an oleophilic/more hydrophobic surfactant mixed
into the oil phase blend of silicone pressure sensitive adhesive
and volatile silicone fluid before adding the water, which has the
more hydrophilic surfactant premixed into it, to the oil phase.
Usually an ionic (anionic or cationic) surfactant, for example an
alkyl aryl sulphonate in amine or alkali metal salt form, is more
hydrophilic than a nonionic surfactant, for example an ethoxylated
fatty alcohol, acid, amine or amide. Where two nonionic surfactants
are used, that containing a higher proportion of ethylene oxide
units to fatty alcohol, acid, amine or amide is generally more
hydrophilic.
[0023] The particle size of the emulsion formed is generally in the
range 200 nanometer (nm) to 50 microns; the lower particle size
emulsions are produced by application of high shear, for example in
a homogeniser, sonolator, microfluidiser or a high shear mixer of
the rotor and stator type.
[0024] In another preferred inversion procedure, the silicone
pressure sensitive adhesive and the volatile silicone fluid are
first mixed with a surfactant and a small amount of water to form a
viscous oil in water emulsion ("thick phase"). The amount of water
added at this stage is generally at least 0.5 percent based on the
total weight of silicone pressure sensitive adhesive and volatile
silicone fluid, preferably at least 1 percent up to 10 or 20
percent. Further water can subsequently be added, for example from
20 or 30 percent up to 100 or 200 percent, to form a diluted
emulsion of suitable viscosity for the desired application.
[0025] Alternatively the emulsion can be formed by a dispersion
process comprising mixing the silicone pressure sensitive adhesive
with the volatile silicone fluid and adding the resulting mixture
to an aqueous solution of the surfactant while shearing.
[0026] We have found that the inclusion of a thickener in the
aqueous phase prior to the mixing of the aqueous phase with the
siloxane composition when using the dispersion process, produces a
more uniform, stable emulsion than without the inclusion of the
thickener. The thickener can for example be a water soluble
polysaccharide such as xanthan gum, a cellulose ether such as
methyl cellulose or hydroxypropyl cellulose, or gum tragacanth, a
carboxyvinyl polymer or polyvinyl alcohol. Such a thickener can be
used in the aqueous phase in an inversion process also.
[0027] The pressure sensitive adhesive emulsion of the invention
delivers performance properties such as controlled tack and
lubrication and can be used for example in paper coatings, such as
adhesive labels and envelope sealing strips, in adhesive modifiers
such as release modifying additives for organic pressure sensitive
adhesives, in personal care applications to give greater
durability, protective qualities, water resistance and barrier
properties, for example in eye cosmetics such as mascara and in
sunscreen formulations as described in U.S. Pat. No. 5,451,610, and
in medical applications such as transdermal drug delivery patches,
described for example in U.S. Pat. No. 5,162,410, or to hold an
active material such as a fungicide to the skin surface. The
avoidance of hydrocarbon based solvents is generally desirable in
medical and personal care applications, and also in paper coating
applications where evaporation of organic solvent can be a fire
hazard.
[0028] For some uses it may be desirable to remove the volatile
silicone fluid from the emulsion before use. In one process
according to the invention for the production of a pressure
sensitive adhesive emulsion of reduced volatile content, an
emulsion as described above is subjected to steam stripping. Steam
or superheated steam is blown through the emulsion with extraction
of volatile materials so that the volatile silicone fluid is partly
or wholly removed from the emulsion, leaving an emulsion of the
silicone pressure sensitive adhesive in water with surfactant
[0029] In an alternative process according to the invention for the
production of a pressure sensitive adhesive emulsion of reduced
volatile content, the emulsion is heated with removal of volatile
material while adding water to the emulsion to compensate for water
which is removed. The emulsion can be fed continuously to a
continuous flow device for vaporizing liquids in which the mixture
is subjected to vaporization in the continuous flow device. The
emulsion can for example be fed to the top of a falling thin film
evaporator or spinning band film evaporator. An overhead fraction
of the volatile siloxane oligomers is continuously removed from the
continuous flow device, while an unvaporized bottom fraction is
continuously removed from the continuous flow device. A preheated
stripping gas such as steam, nitrogen, air, or argon, is fed to the
continuous flow device in a manner that results in either a
cocurrent or countercurrent flow through the device. The
unvaporized bottom fraction consists of an emulsion containing the
silicone pressure sensitive adhesive which is substantially free of
any residual volatile silicone fluid.
[0030] In a further alternative process according to the invention
for the production of a pressure sensitive adhesive emulsion of
reduced volatile content, the emulsion is contacted with a
hydrophobic pervaporation membrane, that is a membrane that
preferentially permeates the volatile silicone fluid. As the feed
liquid flows along the membrane surface, the preferentially
permeated volatile siloxane passes through the membrane as a vapor.
Transport through the membrane is induced by maintaining a vapor
pressure on the permeate side of the membrane that is lower than
the partial pressure of the feed liquid. The pressure difference is
achieved by maintaining a vacuum, or by providing an inert purge
such as air or nitrogen on the permeate side of the membrane. The
permeate vapor is preferably condensed. The condensate is removed
as a two-phase mixture containing primarily volatile silicone and
water. The residue, a silicone pressure sensitive oil-in-water
emulsion depleted of the volatile silicone fluid, exits on the feed
side of the membrane. It is generally desirable to separate the
volatile silicone from the water in the condensed permeate to
facilitate the re-use or disposal of the materials. Suitable
methods for separating volatile silicones from water include
passing the two-phase mixture through a separating device, such as
a settling tank, cyclone, centrifuge, coalescer, separating
membrane, or a combination of such devices.
[0031] The pressure sensitive adhesive emulsion of reduced volatile
content can in general be used in all the applications mentioned
above for the emulsion.
EXAMPLES
[0032] The following examples are set forth in order to illustrate
the invention in more detail.
Example 1
[0033] 60 percent by weight of a pressure sensitive adhesive
comprising 35 parts by weight polydimethylsiloxane, hydroxy
terminated, of viscosity about 13 Pa.s mixed with 65 parts MQ resin
of M/Q ratio in the range 0.6 to 0.9 and a small amount of ammonia
catalyst was mixed with 40 percent octamethyltetrasiloxane to form
a low tack PSA blend. To a single cup Hauschild dental mixer with a
12 second mix cycle was added 37.4 g of the PSA blend and 2.76 g
Stepan Bio-Soft N-300, an anionic TEA-Docecylbenzene sulfonate
surfactant. This was mixed for 1 cycle, then 10 drops deionised
water were added and mixed 1 cycle. Water addition was repeated
until the mixture became inverted (4.34 g water had been added),
forming a thick phase emulsion. This was confirmed to be an oil in
water emulsion that easily dispersed into water. Microtrac UPA 150
particle size analysis showed a trimodal peak with diameter/volume
percent values of: 4.09 microns (24 percent volume), 1.47 microns
(70 percent volume), 0.326 microns (6 percent volume).
Examples 2-4
[0034] Following the procedure of Example 1, three different PSA
polymer types (i) the low tack PSA of Example 1 used in Example 2,
(ii) a high tack PSA containing a higher proportion of
polydimethylsiloxane to resin used in Example 3; and (iii) a medium
tack with an intermediate proportion of polydimethylsiloxane to
resin used in Example 4; were emulsified using the above inversion
process. The PSA's were solvated/diluted with hexamethyldisiloxane,
a linear low molecular weight volatile silicone with a viscosity of
0.65 cSt., rather than octamethyltetrasiloxane as volatile silicone
fluid. A two cup dental mixer unit was used. 123.2 g PSA blend was
mixed with 5.60 g N-300 surfactant and 1.40 g ICI Brij 30, a
nonionic polyethoxylated (4 moles) lauryl ether surfactant, was
added to the formulation as a second surfactant before adding water
(15 drops per cycle). The mix cycle was 20 seconds at full rotation
and planetary rotation speeds. Thick oil in water emulsions were
produced in all cases. Mastersizer particle size analysis showed a
monomodal particle size distribution in all three emulsions. The
mean particle sizes were:
[0035] Example 2--5.78 microns
[0036] Example 3--10.1 microns
[0037] Example 4--9.4 microns
Example 5
[0038] 2340 g of the pressure sensitive adhesive of Example 1 was
diluted with 1260 g hexamethyldisiloxane to form a PSA blend and
was mixed in a Turrello mixer with 60 g Brij 30 surfactant for 10
minutes. 165 g N-300 surfactant was dissolved in 705 g water and
added to the mixer at impeller speed 500 rpm. This was increased to
2600 rpm until the mixture inverted to a thick oil in water
emulsion and mixing was continued for 30 minutes more. The mixer
speed was reduced and the emulsion was diluted with 1464 g water
containing 6 g Kathon.RTM. CG biocide. Mastersizer particle size
analysis showed a monomodal peak with an average particle size of
9.2 microns.
Example 6
[0039] 123.2 g of the PSA blend of Example 5 was mixed with 5.60 g
Brij 35L surfactant, a 72 percent aqueous solution of
polyethoxylated (23 moles) lauryl ether, and 2.10 g Brij 30
surfactant, and then with water using the procedure of Example 2.
9.10 g water was added to form a thick phase oil in water emulsion
which could easily be dispersed into water. Mastersizer particle
size analysis showed a biomodal particle size distribution with
mean particle size of 16.4 microns.
Example 7
[0040] 1.25 g Kelzan xanthan gum thickener was dissolved in 181.25
g water and 13.75 g N-300 surfactant was slowly added. 300.0 g of
the PSA blend of Example 5 was added while the mixer speed was
gradually increased to 1750 rpm. Mixing was continued for 10
minutes, then 3.75 g Brij 30 was added and mixed for 30 minutes.
The aqueous emulsion formed had mean particle size 9.62 microns
with a monomodal distribution. The particle size could be reduced
to below 1 micron by use of a high shear mixer.
Example 8
[0041] The process of Example 7 was repeated omitting a thickener.
The emulsion produced was thinner and not as smooth and creamy as
the emulsion of Example 8, and had mean particle size 28.5 microns
with broad monomodal distribution.
[0042] Other variations may be made in compounds, compositions, and
methods described herein without departing from the essential
features of the invention. The embodiments of the invention
specifically illustrated herein are exemplary only and not intended
as limitations on their scope except as defined in the appended
claims.
* * * * *